This invention relates to a wet shaving razor comprising a cartridge that includes a shaving blade with a cutting edge which is moved across the surface of the skin being shaved by means of an adjoining handle. Conventional safety razors have a blade unit connected to a handle for a pivotal movement about a pivot axis which is substantially parallel to the blade or the blade edge. For example, U.S. Pat. Nos. 7,197,825 and 5,787,586 disclose such a razor having a blade unit capable of a pivotal movement about a pivot axis substantially parallel to the blade(s). The pivotal movement about the single axis provides some degree of conformance with the skin allowing the blade unit to follow the skin contours of a user during shaving. Such safety razors have been successfully marketed for many years. However, the blade unit can fail to remain flat and often disengages from the skin during shaving due to the blade unit's limited ability to pivot about the single axis combined with the dexterity required to control and maneuver the razor handle. The combination of these deficiencies can affect the glide and overall comfort during shaving.
There have been various proposals for mounting a cartridge on a handle to enable movement of the cartridge during shaving with the aim of maintaining conformity of the skin contacting parts of the cartridge with the skin surface during shaving. For example, many currently marketed razors include pivoting mechanisms which enable the cartridges to remain flat throughout the shaving stroke by providing a pivot axis in the center of the cartridge extending parallel to the cutting edges of the elongate blades incorporated in the cartridge. A razor including pivot axis 3 in the center of the cartridge 20 is illustrated in FIG. 1B. As shown in FIG. 1B, as the centrally pivoted cartridge approaches a bump in the skin 2, the blades 16 are compressed into the skin 2 increasing the risk of nicks and cuts which can potentially impact product safety. As a result, pivoting razor cartridges have progressed to forward pivot axis cartridges as illustrated in FIG. 1A having the pivot axis 3 beneath the guard 15 in order to produce a guard heavy cartridge 20. As the forward pivoting razor cartridge traverses the bump shown in FIG. 1A, the blades 16 are free to rotate away from the skin 2 reducing the risk of nicks and cuts. However, the forward pivoting cartridge has its drawbacks in that the guard heavy cartridge impacts the contact that the cartridge makes with the skin as well as the corresponding pressure distribution both of which are important to shaving efficacy and feel.
Throughout the development of razors, the cartridge to skin angle, or CTSA, has been a key measure to better understand contact between the cartridge and the skin. As illustrated in FIG. 1C, CTSA is the angle α between the skin tangent line 4 and the cutting plane 6 which is tangent to the guard 15 and cap 18. A flat CTSA α is desired for optimal cartridge to skin contact and pressure distribution throughout the shaving stroke.
Studies have revealed that CTSA is dependent on the cartridge pivot axis location. It has been found that designing a shaving razor cartridge that can pivot about virtual pivot axis located below the shaving plane and into the skin can provide a flat cartridge to skin angle throughout a shaving stroke. However, pivoting mechanisms are often restricted by the constraints of the cartridge which limit the capability for providing a desirable virtual pivot axis location. For instance, shell bearings are a commonly used pivot mechanism in razor design known to produce virtual pivot axis. An example of a shell bearing capable of producing a virtual pivot axis is disclosed in U.S. Pat. No. 5,661,907. However, shell bearings can rattle and bind leading to poor functionality and a low quality feel. These characteristics are extenuated as the radius of the shell is increased which is also limited to the constraints of the cartridge. Therefore, shell bearings are somewhat limited in their ability to produce virtual pivot axis. Thus, there is a need for a pivoting mechanism for a wet shaving razor capable of producing an optimal virtual pivot axis location that can maintain a flat CTSA throughout the shaving stroke with minimal nicks and cuts. There is also a need for a pivoting mechanism for a wet shaving razor capable of producing an optimal virtual pivot axis location that is not limited to the physical boundaries of the cartridge.